1. Field of the Invention
The present invention relates to a lamp, and more particularly to a light emitting bulb.
2. Description of the Related Art
Because a light emitting diode (LED) has a light emitting efficiency of more than 150 lm/w, and is mercury free and environment-friendly, the LED has gradually been adopted as a main light source for lighting. However, when the current LED bulb, which utilizes a LED light source, is used as a substitute for a “tungsten filament bulb” or so-called “energy-saving bulb,” the following difficulties still exist and arise to challenge the technology thereof:
1. Excessively Small Beam Angle:
A beam angle refers to the effective lighting angle of a bulb within a space. Generally, the beam angle of the “tungsten filament bulb” or so-called “energy-saving bulb” may reach more than 300 degrees. However, currently the beam angle of the LED bulb in the market is about 120 degrees, and rarely goes beyond 180 degrees. One of the reasons why the beam angle of the conventional LED bulb is small is that the LED light emitted pertains to a half-space beam angle, which is similar to a Lambertian light source, and whose beam angle is only 120 degrees (which is calculated with a half-luminance angle thereof, the details of which are described below). It is inferior to the “tungsten filament bulb” or “energy-saving bulb” which has a full-space beam angle. Generally, the light luminance Iv of an ideal Lambertian light source decreases as the beam angle θ between the light luminance Iv and the normal of the LED light emitting plane increases (in which I0 is the maximum luminance obtained when the beam angle θ is 0 degree), with the relation formula thereof:Iv(θ)=I0 Cos θ  (1)
A schematic view thereof is shown in FIG. 1. It is defined that the available beam angle θF thereof is double the luminance angle θH (at this angle, the luminance Iv (θH) thereof is one half of I0), and it be derived from the formula (1) θF=2×θH=2×60=120 degrees.
As shown in FIG. 2, another reason why the beam angle of the conventional LED bulb is small is that the shape and structure of the LED bulb limit the beam angle thereof to within 180 degrees. In a general LED bulb, heat sink fins 22 must be fully distributed between the head 21 of a power input end of the bulb and an LED 20 so as to dissipate heat. The materials composing these heat sink fins 22 are mostly metal materials with good heat dissipation ability, such as: aluminum, copper or an alloy thereof, and additionally, nitride aluminum or oxide aluminum ceramic with good heat conduction ability is also utilized. These materials are all opaque materials, however, and thus the LED bulb is restricted to utilizing a light transmissive material for outputting light rays at a front end portion 23 thereof. As a result, the output of the light generated by the light source LED 20 is limited to a maximum of 180 degrees in the front.
Although there currently exists a conventional technology that uses a secondary optical structure in an LED bulb to manufacture an LED bulb with a beam angle of 300 degrees, the structure thereof is complex, the light emitting efficiency is low, and its uniformity is weak. The schematic structure thereof is shown in FIG. 3.
As shown in FIG. 3, the LEDs 31 are distributed around the entire corresponding circumference, the material of the secondary optical structure 30 is a white reflecting body, and a first layer of reflecting plate 32 and a second layer of reflecting plate 33 are disposed inside the conventional LED bulb. As shown in FIG. 3, for the light ray emitted by the LED 31, a part thereof is reflected by the first layer of reflecting plate 32 into bulb holder direction light 34, another part of light ray is reflected by the second layer of reflecting plate 33 into side direction light 35, and additionally, a large part of the light ray is directly emitted through other manners into front direction light 36, thereby forming an LED bulb having a beam angle of 300 degrees. However, the structure thereof is complex, the light emitting efficiency is low, and its uniformity is weak.
2. Non-Uniform Light Emitting:
Because the light flux of 500˜1000 μm can be reached only when the power required by the LED bulb is approximately 5 W˜10 W, the problems posed by the power and heat conduction of a single-chip LED make it difficult to meet the foregoing requirement. Therefore, LED bulbs generally all use a plurality of chips to meet the foregoing requirement. However, the luminance and chromaticity of these chips are different from each other, leading to non-uniform phenomenon such as light spots or yellow circles on the LED bulb, a problem circumvented by the “tungsten filament bulb”, or “energy-saving bulb”, whose surface light emission is very uniform.
3. Undesired Light Emitting Inefficiency:
Although the light emitting efficiency of an LED chip can currently reach 150 lm/w, and may further reach 250 lm/w in the future, the overall light emitting efficiency of current bulbs is only approximately 50%˜60% of the efficiency of the chip, that is to say, only just 75 lm/w˜90 lm/w. The low overall light emitting efficiency of the bulb can be attributed mainly to three factors: (1) electronic circuit efficiency (currently it has reached 80%, and in the future may reach 90%); (2) temperature (the light emitting efficiency of a chip decreases as the temperature increases, and generally whenever the temperature increases by 10° C., the light emitting efficiency thereof decreases approximately by 2%); and (3) low light emitting efficiency of the bulb structure (generally below 80%).
4. Undesired Heat Dissipation Effect:
The structure of the conventional LED bulb is shown in FIG. 2, in which the sum of the area of the heat dissipation region of the heat sink fins 22 and the area of the light emitting region of the front end portion 23 is a constant value. If the heat dissipation region is increased, the area of the light emitting region is decreased; inversely, only when the heat dissipation region is decreased can the light emitting region be increased. Thus, a difficult choice is presented. It is generally decided that the heat dissipation region and the light emitting region each account for approximately 50%. The light emitting region limits the heat dissipation region, and as a result, the heat dissipation effect is hampered, the light emitting efficiency is decreased, and the service life of the LED 20 is shortened. Another problem exists. As shown in FIG. 4, because a lamp shade 41 of a lamp mounted with a conventional LED bulb limits air convection of a heat dissipation region 42 thereof, the heat dissipation becomes excessively deficient. As shown in FIG. 4, a glass lamp shade 41 causes hot air to converge at a part of the heat dissipation region 42 of a conventional LED bulb, rendering it unable to dissipate heat. Although air convection at the light emitting region 43 of the conventional LED bulb is intrinsically good, this air convection is unable to fulfill its role in heat dissipation, which causes the temperature of the LED chip to become very high.
5. Excessively Heavy Weight:
In the conventional LED bulb shown in FIG. 2, the heat sink fins 22 that must be disposed to assist in heat dissipation increase the weight thereof to approximately 150 g, which is excessive compared with the weight of the general “tungsten filament bulb”, which is only approximately 50 g.
6. Undesired Appearance:
The light emitting region of the general “tungsten filament bulb” or “energy-saving bulb” is a complete sphere, and the shape thereof is aesthetic and smooth. However, in the conventional LED bulb shown in FIG. 2, a large part of the heat dissipation region is exposed beside the light emitting region thereof. Its strange resultant shape makes the conventional LED a less likely option for general household lighting.
7. Increased Electric Shock Risk Caused by the Metal Heat Dissipation Region:
Conventional LED bulbs have gradually begun to adopt high-voltage direct-current or alternating-current power sources for the LED, but the power supply thereof is directly input after the alternating-current is rectified. If the heat sink fins thereof are made of a metal material, electric shock is easily caused while a ground terminal is inversely inserted. Therefore, an isolation transformer must be utilized to prevent electric shock, which increases power loss and cost.
8. Excessively High Price:
Currently, the price of an LED chip has been reduced to 300˜400 lm/USD; that is, the lumen quantity of each dollar has reached 300˜400 lm, and in future the price may be reduced to 1000 lm/USD. Although a bulb chip having 1000 lumens currently only requires 2.5˜3.3 dollars, because the overall efficiency is only 50%˜60% of the light emitting efficiency, the actual cost for using an LED chip still reaches 5˜7 dollars. After adding the heat sink fins and the electronic circuit, the unit cost is still more than 10 dollars, a barrier which prevents it from becoming more widely used.